If you try to edit the email address of a synchronized user’s mailbox in Exchange Online Admin Center, you’ll sometimes see the following error message:
The Root Cause of Email Address Type Update Failed
As the error message hints, the object you try to modify is synchronized from your on-premises Active Directory.
This makes your on-premises Active Directory authoritative for a number of attributes, including the email address.
To modify the email address of a synchronized user’s mailbox, you need to make the changes on the user object in the on-premises Active Directory.
You can do this in several ways. The easiest way, by far, is using the Easy365Manager snap-in for Active Directory Users & Computers:
The Easy365Manager snap-in for AD Users & Computers will check the email address’s validity and that the email address is unique across your organization.
Additionally, you can quickly trigger an Azure AD Connect synchronization directly from user properties, without the need to use PowerShell.
For alternative options to modify this attribute, read this article.
With Easy365Manager, you can perform all daily Office 365 mailbox administration directly from AD user properties.
This includes managing calendar delegation, which is usually only possible using rather complex PowerShell scripting:
Easy365Manager makes no changes to your infrastructure, and you can install it in less than a minute.
Easy365Manager builds on the familiar interface of AD Users & Computers, so you can start using it immediately.
Download a fully-functional 30-day trial of Easy365Manager here.